FIGS. 14 and 15 show a conventional inclination sensor. FIG. 14 is a longitudinal sectional view of the inclination sensor, whereas FIG. 15 is a longitudinal sectional view taken along lines XV-XV in FIG. 14. The inclination sensor X shown in the figures includes a case 91, a pair of light receiving elements 92a, 92b, a light emitting element 93, a ball 94 and leads 95, 96. As shown in FIG. 15, the paired light receiving elements 92a, 92b and the light emitting element 93 face each other across a space 91a defined in the case 91. The ball 94 is accommodated in the space 91a. 
The paired light receiving elements 92a and 92b are mounted on the lead 95. The light emitting element 93 is mounted on the lead 96. The leads 95 and 96 include external leads 95a and 96a projecting from the case 91. The external leads 95a and 96a are used for mounting the inclination sensor X onto a circuit board S. When the light receiving elements 92a and 92b receive light emitted from the light emitting element 93, the light receiving elements 92a and 92b output light receiving signals to indicate the light reception.
As shown in FIG. 14, when the circuit board S on which the inclination sensor X is mounted is substantially parallel to the horizontal surface, the ball 94 is located on the bottom of the space 91a in FIG. 14. In this state, the light emitted from the light emitting element 93 is not blocked by the ball 94, and hence, received by both of the paired light receiving elements 92.
When the circuit board S is inclined clockwise through an angle not less than the angle θ in FIG. 14, the ball 94 moves within the space 91a to a position indicated by the double-dashed line A. In this state, the ball 94 is located in front of the light receiving element 92b. Thus, of the light emitted from the light emitting element 93, the part which is to reach the light receiving element 92b is blocked by the ball 94. Conversely, when the circuit board S is inclined counterclockwise through an angle not less than the angle θ in FIG. 14, the ball 94 moves within the space 91a to a position indicated by the double-dashed line B. In this state, the ball 94 is located in front of the light receiving element 92a. Thus, of the light emitted from the light emitting element 93, the part which is to reach the light receiving element 92a is blocked by the ball 94.
Thus, by monitoring the light receiving signals outputted from the light receiving element 92a, 92b, it is possible to detect the direction in which the circuit board S, i.e., the inclination sensor X is inclined within a plane which is parallel to the sheet surface of FIG. 14, i.e., within the vertical plane.
The inclination sensor X is mounted to the circuit board S by using the external leads 95a and 96a projecting from the case 91 so that the inclination sensor X stands upright on the circuit board S as shown in FIG. 14. Thus, the plane which contains inclination direction to be detectable by the inclination sensor X (hereinafter referred to as the “detection target plane”) is perpendicular to the mount surface of the circuit board S. Thus, the inclination sensor X cannot detect the rotation of the circuit board S made within a plane which is generally parallel to the mount surface.
An inclination sensor may be incorporated in a digital still camera whose body is in the form of a horizontally elongated rectangular parallelepiped. In this case, the sensor detects whether the image to be captured is vertically elongate or horizontally elongate. Based on the detection result, the orientation of the image to be displayed at the liquid crystal display maybe automatically switched. Specifically, when the body of a digital camera is held horizontally, a horizontal image is captured. When the camera body is held vertically, a vertical image is captured. Thus, with an inclination sensor mounted to a circuit board incorporated in the digital camera, it is possible to detect the inclination of the body of the camera within a vertical plane, thereby deciding whether the body of the camera is held-horizontally or vertically. Based on the detection result, the orientation of the image to be displayed at the liquid crystal display can be automatically adjusted so as to correspond to the image to be captured.
However, the circuit board carrying the inclination sensor is often disposed in parallel to the longitudinal direction of the body. When the cameral body is inclined within the vertical plane in taking a picture, the circuit board rotates, with the mount surface standing generally vertically. As noted above, the detection target plane of the inclination sensor X is a plane which is perpendicular to the mount surface of the circuit board S. Thus, when the circuit board S on which the inclination sensor X is mounted is incorporated in a camera body, the detection target plane of the inclination sensor X in the photographing posture is generally parallel to the horizontal surface. Thus, even when the camera body is inclined within the vertical plane in photographing, the ball 94 in the inclination sensor X does not move to the position A or B shown in FIG. 4. In this sense, the conventional inclination sensor X is not suitable for detecting the photographing posture of a digital camera.
Patent Document 1: JP-A-H11-14350